In the assembly of a semiconductor package to a printed wire board, an integrated circuit chip is attached to a metal lead frame, in many case, a copper coated leadframe, with adhesive and wire bonding, and the whole assembly then encapsulated in a molding resin. After encapsulation, the outer leads of the lead frame are attached to a printed circuit board. During storage and transportation, any metal, and particularly, copper surfaces are subject to oxidation with exposure to air. Such uncontrolled oxidation is detrimental to adhesion between the lead frame and any adhesive or molding compound, and subsequently detrimental to the reliability of the whole lead frame package. To alleviate this problem, lead frame manufacturing routinely includes a process to apply an antioxidant coating onto the lead frame surface.
Nitrogen-containing compounds such as benzotriazoles are commonly used as antioxidants and corrosion inhibitors for copper and copper alloys in many environments and applications. The aromatic moiety of the benzotriazoles is believed to help reinforce a parallel alignment onto the metal substrate and the nitrogen rich triazole to serve as an adhesion promoter. When benzotriazole is applied as a coating, the copper surface is blocked from direct contact with air and moisture, which inhibits oxidation to certain level. However, the presence of benzotriazoles is suspected of interfering with the bonding process during the die attach, wire bonding, encapsulation, and final soldering operations in the manufacture of the semiconductor package and its attachment to a printed circuit board. Such interference probably is caused by the physical separation between the copper substrate and die attach or molding compound and by the absence of any chemical bond between the antioxidant layer and die attach or molding compound. Benzotriazole is also known to be thermally unstable at the temperatures that are used for die attach adhesive curing and testing, which are typically at 170° C. and above. The decomposition products and processes of benzotriazoles remain little understood, and hence unpredictable in terms of their interference in the reliability of the lead frame packages.